Clinical microbiology and hospital infection control: quantitative BAL culture: practice question

A Microbiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Microbiology · Clinical microbiology and hospital infection control: quantitative BAL culture

Sample item

In a ventilated patient with suspected pneumonia, quantitative culture of bronchoalveolar lavage fluid is performed. Growth above which threshold is conventionally taken to indicate pneumonia?

A100 CFU/mLB100,000,000 CFU/mLC1,000,000 CFU/mLD10,000 CFU/mL

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. 10,000 CFU/mL

Quantitative cultures separate infection from airway colonisation. A conventionally used threshold for bronchoalveolar lavage is 10,000 CFU/mL (10^4), while tracheal aspirates use a higher cut-off of about 10^6.

Option by option

A. 100 CFU/mL
100 CFU/mL is within the range of colonisation.
B. 100,000,000 CFU/mL
10^8 CFU/mL is far above any diagnostic cut-off.
C. 1,000,000 CFU/mL
10^6 CFU/mL is the threshold usually applied to tracheal aspirates.
D. 10,000 CFU/mL (correct)
Correct. Growth of at least 10^4 CFU/mL in lavage fluid is the usual threshold.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is D, 10,000 CFU/mL. Quantitative cultures separate infection from airway colonisation.

Why is "100 CFU/mL" not the answer?

100 CFU/mL is within the range of colonisation.

Why is "100,000,000 CFU/mL" not the answer?

10^8 CFU/mL is far above any diagnostic cut-off.

Why is "1,000,000 CFU/mL" not the answer?

10^6 CFU/mL is the threshold usually applied to tracheal aspirates.

What concept does this question test?

It tests Clinical microbiology and hospital infection control: quantitative BAL culture in Microbiology. A conventionally used threshold for bronchoalveolar lavage is 10,000 CFU/mL (10^4), while tracheal aspirates use a higher cut-off of about 10^6.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Clinical microbiology and hospital infection control: quantitative BAL culture?

Make a one-line identity card for each organism: shape and stain, defining test, toxin, disease and drug. Then use the flashcards and the other Microbiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.